Active dust devils in Gusev crater, Mars: Observations from the Mars Exploration Rover Spirit

Abstract

[1] A full dust devil ''season'' was observed from Spirit from 10 March 2005 (sol 421, first active dust devil observed) to 12 December 2005 (sol 691, last dust devil seen); this corresponds to the period L s 173.2°to 339.5°, or the southern spring and summer on Mars. Thermal Emission Spectrometer data suggest a correlation between high surface temperatures and a positive thermal gradient with active dust devils in Gusev and that Spirit landed in the waning stages of a dust devil season as temperatures decreased. 533 active dust devils were observed, enabling new characterizations; they ranged in diameter from 2 to 276 m, with most in the range of 10-20 m in diameter, and occurred from about 0930 to 1630 hours local true solar time (with the maximum forming around 1300 hours) and a peak occurrence in southern late spring (L s $ 250°). Horizontal speeds of the dust devils ranged from <1 to 21 m/s, while vertical wind speeds within the dust devils ranged from 0.2 to 8.8 m/s. These data, when combined with estimates of the dust content within the dust devils, yield dust fluxes of 3.95 Â 10 À9 to 4.59 À4 kg/m 2 /s. Analysis of the dust devil frequency distribution over the inferred dust devil zone within Gusev crater yields $50 active dust devils/km 2 /sol, suggesting a dust loading into the atmosphere of $19 kg/km 2 /sol. This value is less than one tenth the estimates by Cantor et al. (2001) for regional dust storms on Mars.

In situ measurements of particle load and transport in dust devils

“…Given that these results were not calculated from in-situ measurements they are still faily closely matched to our "peak" flux measurements, although they are a much higher than our mean values. We note that the calculated vertical wind speed used by Ferri et al (2003) is 20ms -1 , which seems high compared to most authors' estimates for martian dust devils Greeley et al, 2006: Greeley et al, 2010.…”

“…Nevertheless, if the local climate remained stable over many thousands of years and dust devils were persistently active throughout that time then they could be responsible for meters of deflation. This could certainly be the case for Mars if dust devil flux rates are similar to Earth, as suggested by observations and simulations in the lab (e.g., Greeley et al, 2006;Greeley et al 2010;Neakrase et al, 2010), especially given the lack of competing erosional mechanisms.…”

“…Thomas and Gierasch (1985) measured a dust load of ~ 30 mg m -3 ; Metzger et al (1999) found a range from 10 to 100 g m -3 . Greeley et al (2006) published data only for estimated flux and again particle loads cannot be estimated from their data without attempting to back-calculate particle loads based on cited average vertical wind speeds and flux data. Greeley et al (2010) Over the past ten years we have performed in-situ sampling and analyses of over 100 dust devils (e.g.…”

“…Oke et al, (2007) presents measurements of size-frequency distributions of samples particles but does not relate this to particle loading or flux. More attempts have been made to estimate dust load for martian dust devils using estimates of optical depth from orbit (Thomas and Gierasch, 1985) and the surface Greeley et al, 2006;Greeley et al, 2010). Thomas and Gierasch (1985) measured a dust load of ~ 30 mg m -3 ; Metzger et al (1999) found a range from 10 to 100 g m -3 .…”

Studies of Dust and Discharges around a Martian Rover with Onboard Hazard Analyses using Electromagnetic and Acoustic Wave Measurements

“…Low-frequency E-M and AW are important for monitoring atmospheric events, because these disturbances can propagate for more than 100 km; at lower frequencies and higher amplitudes, this propagation distance could increase to more than 1000 km, depending on the frequency. An example is the infrasound shock wave propagation induced by the Chelyabinsk meteorite fall on Feb. 15,2013, in Russia.…”